1. Field of the Invention
The invention relates to the field of sphere or pig detection devices used to measure flow and other conditions in a pipe. In particular, the invention relates to an improved sphere detection switch assembly which operates in conjunction with spheres running along a pipe to accurately measure the flow rate of fluids moving through the pipe. The invention also relates to an improved switch assembly which may be used to detect the position of inspection and/or maintenance pigs running along a pipe.
2. The Prior Art Background
Sphere detection switches are well known for accurately measuring flow in pipeline installations. These devices are typically valuable to facilitate the measurement of the time it takes for a sphere running along the inside of a pipe to travel between two spaced sphere detection switches. The volume between the detection switches is known, and therefore the volumetric flow rate may be determined simply by measuring the time interval between the time the sphere passes the first switch and the time the sphere passes the second. Known switches typically measure such time interval using a probe shaft having an end which protrudes into the pipe. As the sphere moves along the pipe, it encounters the end of the probe shaft and the outer surface of the sphere acts as a camming surface to push the end of the shaft out of its path in the pipe. This movement translates into longitudinal movement of the entire probe shaft. The probe shaft is equipped with a centrally disposed activation portion, usually in the form of an annular collar extending around the probe shaft. When the shaft moves longitudinally, this activation portion is moved into a detection zone where its presence is detected by a detection surface of a detection element. Typically, the presence of the activation portion in the zone is detected because it disrupts a magnetic field established in the zone by the element. The disruption of the magnetic field results in the generation of an electrical signal which is utilized by a timing mechanism to determine the precise time interval between switches.
Similar devices have been used to detect the position of maintenance and/or inspection pigs.
One of the shortcomings of prior art detection switches in this field results from the buildup of debris, and in particular metallic debris, on the detection surface of the detection element. Suffice it to say that the buildup of debris on the detection surface may interfere with the magnetic field and thereby the accuracy of the timing and/or detection procedure. Another shortcoming is that prior art switch devices have universally employed metallic bearing surfaces to support and guide the longitudinal movement of the probe shaft. This metal-to-metal contact creates additional friction that interferes with the movement of the probe shaft to thereby disturb the accuracy of the generated signal and often results in the generation of metallic debris which is then free to accumulate on the detection surface.
The shortcomings present in prior art devices as described above are alleviated, if not completely eliminated, by the present invention which provides a sphere or pig detection switch assembly adapted for being mounted on a pipe through which a sphere or pig will run. The detection switch assembly may desirably include an elongated, hollow main body portion presenting an elongated chamber therein. The body portion also defines a detection zone positioned alongside the chamber and generally will include mounting structure for a detection element that includes a detection surface to facilitate the mounting of the element with the detection surface thereof adjacent the detection zone for the purpose of providing a magnetic field in the zone.
The detection switch assembly of the invention also may include an elongated probe shaft disposed mainly within the chamber. The probe shaft may be equipped with a centrally disposed activation portion and the same may desirably be mounted for longitudinal movement within the chamber from a first position with said activation portion spaced from the detection zone to a second position with said activation portion at said detection zone. The probe shaft also may have an inner terminal end that protrudes into a pipe upon which the detection switch assembly is mounted when the probe shaft is in its first position. This inner terminal end may be configured, arranged and positioned so that it will be contacted and pushed toward said chamber by a pig or sphere running along a pipe upon which the switch assembly is mounted, whereby to cause the probe shaft to move from its first position to its second position.
In accordance with the principles and concepts of the invention, the detection switch assembly of the invention also may include a wiper element carried by the probe shaft in a position to wipe debris from a detection surface positioned adjacent said zone as the probe shaft moves from its first position to its second position under the influence of contact between a pig or sphere and said inner terminal end of the probe shaft.
In another form of the invention, the same provides a similar sphere or pig detection switch assembly that includes a pair of non-metallic, rigid guide bushings for the probe shaft. One of these guide bushings is disposed in generally surrounding relationship to an inner length of the probe shaft and another one of the guide bushings is disposed in generally surrounding relationship to an outer length of the probe shaft. These bushings are adapted and arranged to support and guide the probe shaft as it moves longitudinally from its first position to its second position so that metal to metal contact is avoided during such movement.
In yet another form of the invention, the detection switch assembly may include the non-metallic, rigid guide bushings as well as the wiper element described above.
Desirably, in accordance with the preferred embodiments of the invention, the chamber of the main body may be cylindrical and the activation portion may be annular. In addition, the wiper element may be annular, disposed so as to surround the outer length of the probe shaft and located in contact with a shoulder on the activation portion of the probe shaft.
In addition, the detection surface may desirably be flat and the wiper element has an outer peripheral edge which is located at a distance of from about 0.0001 to about 0.005 inch from said detection surface.
Furthermore, the bushings may each include an inner circular hole and the inner and outer lengths of the probe shaft may be circular in transverse cross-sectional configuration. Ideally, the bushings may be made of a hard, frictionless plastic material.
In accordance with the invention, the outer peripheral edge of wiper element and the detection surface may desirably be configured such that any debris which may be present on the surface in sufficient quantity to interfere with the detection of the presence of the activation portion at the detection zone is wiped from the detection surface when the peripheral edge passes the detection surface during movement of the probe shaft from said first position to said second position.